The present invention generally relates to data reproducing circuits, and more particularly to a data reproducing circuit which nullifies a series of data when dropout is detected in a data signal picked up from a recording medium, and supplies only a correct data having no dropout to an external circuit.
Recently, apparatus have been realized which are capable of reproducing a recorded information signal from a rotary recording medium (hereinafter simply referred to as a disc). The disc is recorded with a main information signal such as a video signal and an audio signal, on a spiral track formed on the disc. The reproducing apparatus scans over the disc with a reproducing stylus having an electrode, for example, and reproduces the recorded main information signal as variations in electrostatic capacitance between the electrode of the reproducing stylus and the disc. In the above type of a disc, for example, four fields of video signal is recorded for one track turn of the disc. A chapter data indicating a program number of the main information signal, is recorded at the seventeenth H (H indicates a horizontal scanning period) from a rise of a vertical synchronizing signal, within a vertical blanking period in each field. Furthermore, a time data indicating a recorded position (address) of the main information signal from the position where the recording was started in reproducing time, is recorded on the disc at the eighteenth H. For example, these data are data signals using the biphase space code.
In the above type of a disc, when dropout exists in the data signal picked up from the disc by the reproducing stylus, this data signal is reproduced as a signal having an erroneous data content. Accordingly, when the signal having the erroneous data content due to dropout and the like is used, there is a disadvantage in that erroneous chapter data and erroneous time data are obtained.
On the other hand, the video signal of four fields is recorded in one track turn of the disc as described above. Hence, there are four vertical blanking periods in one track turn of the disc. This means that signals having the same data content are recorded at four positions for one track turn of the disc. Therefore, when data reproduction is erroneously performed due to the above dropout and the like, no hindrance will be introduced even if the erroneous data is not used and the data at other vertical blanking period positions within the same track turn is used instead.